1. Field of the Invention
The present invention relates to a dust-proof structure for measuring tools. In particular, the present invention relates to a dust-proof structure for electronic components in measuring tools such as an electronic caliper, a micrometer, a dial gauge and a scale unit.
2. Description of Related Art
In measuring tools such as an electronic caliper, a micrometer, a dial gauge and a scale unit, electronic components are accommodated in a dust-proof space so as to prevent malfunction and damage of the electronic components due to dust or the like.
For instance, Patent Literature 1 (JP-A-8-193848) discloses a dust and water proof structure for measuring tools.
As shown in FIG. 10, the dust and water proof structure includes: a case 110 being provided with a transparent protection plate 112 in a bottom wall opposed to an opening 111; a solar cell unit 120 being accommodated in the case 110 through the opening 111 of the case 110 and having an outer circumference surrounded by a first packing 121; an internal frame 130 including a bottom wall 131 pressing the first packing 121 of the solar cell unit 120 against the bottom wall of the case 110, and a flange 132 projecting near an opening end of the case 110; a display device 140 being provided on an inner bottom surface of the internal frame 130; a substrate 150 being attached to the flange 132 of the internal frame 130 via a second packing 151 to close the opening 111; and a screw 170 being tightened to integrally secure the substrate 150 and the flange 132 of the internal frame 130 to the case 110 and loosened to detach the substrate 150 and the flange 132 of the internal frame 130 from the case 110.
With the above dust and water proof structure disclosed in Patent Literature 1, even when dust or the like enters a gap between the protection plate 112 of the case 110 and the solar cell unit 120 and a gap between the internal frame 130 and the display device 140, these components can be detached for cleaning by loosening the screw 170, thereby preventing deterioration in appearance due to such dust or the like.
Based on the assumption that dust enters the structure during assembling or the like, the technique disclosed in Patent Literature 1 is intended to disassemble the structure for cleaning to prevent deterioration in appearance. However, it is nonproductive to disassemble the once-assembled structure and reassemble it.